This invention relates to a feedback control system for the control of a fuel supply rate to an internal combustion engine, and more particularly to a fuel supply control system comprising an electrostatic flow rate control apparatus which has no mechanically moving part and a flow rate detector which provides an electrical signal.
A fuel supply system for an internal combustion engine comprises a fuel metering device or an air-fuel proportioning device such as a fuel injector or a carburetor to feed the engine with an air-fuel mixture of an intended air/fuel ratio. In recent years, there is a strong and growing demand for improvement on the precision in the control of the air/fuel ratio, particularly for automotive internal combustion engines, since the improvement is almost a requisite to the success in reducing harmful components of the exhaust gas and lessening the fuel consumption per mile to the extent of fully meeting current requirements without a substantial sacrifice of the operability of the engines.
To maintain the air/fuel ratio exactly at an intended value, there is a need of precisely controlling the rate of fuel supply in accordance with changes in the quantity of air being admitted into the engine. It is a current trend in automotive internal combustion engines, therefore, to employ an electronic fuel supply control system which includes an electromechanical device such as an electromagnetic valve for minutely varying the fuel supply rate and an electronic control unit for operating the electromechanical device based on certain variables related to the admission of air into the engine or operating condition of the engine. In practical applications, however, the performance of this type of fuel supply control system is not always fully satisfactory because there are limits to the responsiveness and durability of the electromechanical flow rate control device.
In this connection, an electrostatic apparatus for controlling the volumetric flow rate of a liquid which apparatus has no mechanically moving part is disclosed in Japanese patent application Nos. 51(1976)-51694, 51(1976)-73874, 51(1976)-62911 and U.S. patent application Ser. Nos. 794,137 by S. Suzuki and 801,394 by K. Masaki. This flow rate control apparatus comprises a pair of electrodes disposed in a liquid passage with a short interval therebetween, a high voltage DC power supply and a controller to vary the magnitude and/or polarity of a DC voltage applied to the electrodes. When a DC high voltage of 1-100 kV is applied to the electrodes, an electric field is produced in the liquid between the electrodes and causes the liquid particles to be charged with the result that a propulsive stress is imposed on the liquid. Consequently the liquid in the electric field migrates toward one of the electrodes. The direction of the liquid flow thus produced with respect to the porality of the voltage applied to the electrodes depends on the kind of the liquid. For example, gasoline tends to flow toward the positive electrode. If the two electrodes are disposed in a stream of gasoline with the interval therebetween in the directon of the stream, the linear velocity of the stream and hence the volumetric flow rate of the gasoline can usually be enhanced by the application of a DC high voltage to the electrodes with the downstream side electrode as a positive electrode and can be lowered by reversing the polarity. The scale of the enhancement or lowering can be controlled by varying the magnitude of the applied voltage.